For the purpose of beautiful appearance and size reduction, a mobile terminal, such as a mobile phone, currently has a built-in antenna configured to transmit and receive signals. The built-in antenna requires that the mobile phone should have a housing not blocking signal transmission and reception. However, metal housings instead of plastic housings are gradually applied to mobile terminals such as mobile phones, since the metal housings have more beautiful appearances, abrasion resistance, and scratch resistance. In this case, in order to enable signal transmission and reception, a slot should be formed in the metal housing of the mobile terminal and filled with insulating material such as plastic, but the insulating material received in the slot has a color quite different from the anodized surface of the metal, which seriously destroys the unity of the housing.